Method of treating oil wells to prevent water coning



1 6 6 3 g} CROSS REFERENCE sEAEEQEE 1968 E. c. DONALDSON ETAL 3,369,605

METHOD OF TREATING OIL WELLS TO PREVENT WATER CONING Filed Aug. 19, 1966 5 Sheets-Sheet 1 INVENTORS Erle C. Donaldson Calvin H. Riggs A TTURIVEYS Fe 20.-1 96 a. c. DONALDSON any 3.35 .5 mm or-fraanmo on. wsuus mfrnsvannjsa comm; I Filed Aug; 19. I I I I J United States Patent 3,369,605 METHOD OF TREATING OIL WELLS TO PREVENT WATER CONING Erle C. Donaldson and Calvin II. Riggs, Bartlesville,

0kla., assiguors to the United States of America as rep resented by the Secretary of the Interior Filed Aug. 19, 1966, Ser. No. 574,289 8 Claims. (Cl. 166-42) ABSTRACT OF THE DISCLOSURE The existence of water coning is eliminated or prevented in oil producing wells by separately fracturing the formation in the oil producing zone and the transition zone of oil and water and in the water zone, cementing the middle fracture, and injecting a gas through the lower fracture. The gas may be injected between or during pcriods'of oil production.

urated. water producing formation. Under static, non

producing conditions the water having a greater density is found beneath the oil producing formation. During production, however, a pressure drop is formed near. the

well, causing both oil and water to fiow radially toward the well bore. The small difference in density 'and large difference in viscosity between the water and the oil gives rise to upwardly directed pressure gradients around the well. This difference in pressure causes the water to rise a substantial height above the normal or static oil-water interface and forms conical column around the well bore within the normal oil producing region. This phenomenon is known as water-coning. The result of waterconing in a producing well is a rise in the water to oil production ratios, a consequent lowering of oil production. an increase in the cost of lifting the oil, an additional expense incurred in separating the water from the oil. an increase in corrosion problems and expense of water disposal. As production continues, the water level rises even further and the water cone grows in size. Eventually a point in the production history is reached when production of oil from the well is no longer economical.

Several methods of suppressing water-coming in oil wells have been suggested. One method involves reducing the depth of the oil well and recovering oil only from the top of the formation. This method often unduly restricts oil recovery and is not considered a satisfactory solution, especially in formations having thin oil pay zones. Another method is to bottom the well in a formation substantially impermeable to water. However, many wells do not have the water-impermeable formation neccssary for this method. Other methods comprise depositing cement in the well bore adjacent the water-producing formation up to the water-oil interface. These methods have not been found effective to eliminate or greatly reduce water-coning as the water continues to intrude into the oil producing region. Still other methods comprise forcing gas and sealing materials into the water producing zone. With these methods, the sealing material often intrudcs into the oil zone thereby reducing the oil production rate. In addition, it has also been suggested to ice fracture the well at the oil-water interface and to fill the fracture with a water impermeable cement early in the production history. However this procedure at best only slows down the formation of a water cone and has been found very difficult to adopt as it is usually not possible to position the fracture in the well with the degree of accuracy required.

Accordingly, it is an object of this invention to provide 'an improved method for increasing oil production from underground formations.

Further, it is an object of this invention to decrease the water/oil production ratio of a well having both water and oil producing formations.

Still further, it is an object of this invention to provide an improved method of overcoming water-coming in oil wells having both water and oil producing formation.

Still further, it is an object of this invention to increase the oil production of a well having both water and oil producing formations while overcoming water-coning.

1 These and other objects of the invention will become apparent from the following disclosure wherein reference is made to the figures of the accompanying drawlng.

FIG. 1 schematically illustrates the phenomenon of water-coning.

FIG. 2 schematically illustrates a well which has been fractured in accordance with the present invention.

FIG. 3 schematically illustrates the method of the present invention in operation.

In accordance with the present invention oil production is increased and water-coning is overcome by the use of selectively positioned horizontal fractures in combination with gas injection. If the well to be treated is undergoing production, the production is halted, then a first horizonthe first fracture or the third fracture or both may be filled with a suitable propping agent, for example, metal pellets, glass beads, sands, or shells, to insure a steady fiuid fiow through these fractures. A packer is then installed within the well casing to divide it into an upper section communicating with the oil zone and a lower section communicating with the water zone. A tube is extended through the packer and into the lower portion of the well. Gas is forced under pressure, down the tubing and into the lower portion of the well. The pressurized gas leaves the well bore by way of the lowest fracture which extends into the water zone. As it leaves the area of the well bore the gas permeates through the surrounding s'ands displacing the water in a downward and outward direction from the well. The low density of the gas causes it to rise but the impermeable cemented fracture acts as a barrier to this upward travel and causes the gas to move away from the well pushing the water into the more remote areas of the fomiation. Above the cemented zone the gas moves toward the well bore thereby depressing the water cone and displacing oil into the oilzone frac- V ture. Any of the gas not entering'the oil zone fracture rises to the top of the oil formation until it encounters the cap rock." There the gas collects forming a pocket beneath the rock and in doing so displaces oil downward, in the manner of a gas driven injection well, toward the oil zone fracture.

After the water-cone has been dissipated to an appreciable extent by the injection of gas through the tubing, the production of oil may be re-established and the gas injection may continue simultaneously with oil recovery. Control of the tendency toward further coning can be established by continuous injection of a small quantity of gas. Alternatively, the well may be intermittently treated by gas injection whenever the water/oil ratio increases to an undesirable level.

A number of gases may be used in the present invention. Suitable gases include air, natural gas, compressed exhaust gases from a gas or gasoline engine, or gas mixtures of combustion products such as flue gas.

Referring now to the drawing, FIG. 1 represents a well in which there is water-coning. In that figure, well casing 1 extends through cap rock formation 2, and oil producing formation 3 to a water producing formation 4. Under static conditions the water-oil interface is found at 5. Dur. ing production, oil is drawn toward the well bore and enters the casing through perforations 6. As previously explained this flow of oil causes a pressure drop in the lower portions of the oil producing region near the well bore. The small difference in density and greater difference in viscosity between the water and oil allows water in the vicinity of the wall to rise forming a water cone 7. As production continues, the water-oil zone rises as the water cone rises thereby excluding a large amount of oil from the pay zone and causing a substantial increase in the water/ oil production ratio.

Referring to FIG. 2 of the drawing, there is schematically illustrated a well which has been modified by fracturing in accordance with the present invention. The first fracture 8 is formed horizontally in the oil producing region 3. This fracture may be formed by injection through one of the perforations (6) and may be filled with conventional propping agents, for example, metal pellets, glass beads, sands or shells, as shown at 9. The second fracture 10 is formed horizontally through the water-oil transition zone 11 defined by the water cone 7. This fracture is filled with an impervious material 12 such as cement. A third fracture 13 is made horizontally in the water producing zone 4. It may also be filled with a conventional propping agent 14 such as used in fracture 8.

Referring now to FIG. 3, there is shown a schematic illustration of the method of the present invention. 1 represents a well bore casing extending through a cap rock formation 2, an oil producing formation 3 and into a water producing formation 4 as previously described, the well is fractured at 8, 10 and 13. A tube 15 is fitted with packer 16 and is placed within well bore 1 so that the lower end of tube 15 extends to the vicinity of fracture 13 and so that packer 16 divides well bore 1 into an upper portion 17 communicating with the oil producing formation 3 and a lower portion 18 communicating with the water producing formation 4. A gas is forced through tube 15 into the portion of the well bore 18 communicating with the water producing region. The gas leaves the well bore 1 via fracture 13 pushing water away from the well. The low density of the gas causes it to rise in the formation. The impermeable cemented fracture 10 serves as a barrier for a portion of the rising gas and thereby aids the gas in displacing the water downwardly and outwardly away from the well bore. A portion of the gas rises around the cement fracture l and travels toward the well bore 1 in the area between fractures 8 and 10, thus displacing the uppermost portion of water cone 7. Some of this gas will enter fracture 8 along with the oil. However, this will not adversely affect oil producing as the benefit of reducmg thewater/ oil ratio greatly outweighs the inconvenience of having a portion of the gas enter the product stream.

Another portion of the gas rises to the top of oil formation 3 and collects under cap rock 2. The pressure exerted by this pocket of gas 19 serves to force additional oil into the well via fracture 8.

Although the practice of this invention has been described in terms relating to the preferred embodiment of overcoming water coning in a well that has developed a high water/ oil ratio through production, the order of steps taken according to the present invention may be altered so as to provide for inhibition of water coning in newly formed wells.

With a newly formed well, fracture 10 may be formed and cemented at or slightly above the water/ oil interface before production. The formation of the cemented fracture at that time will aid in inhibiting the rise of a water cone. Likewise fracture 8 may be formed at any time before or during the production history to enhance the flow of 011 and reduce pumping pressure.

Furthermore, the present invention is also applicable to producing wells which may have one or more of the fractures required by the method already formed. To apply the present invention to these wells, the wells are further fractured, divided into upper and lower portions by a packer and gas is injected into the lower portion In any case, treatment of wells by the present invention may be practiced intermittently whenever the water/oil ratio rises to an undesirable level or in a continuous manner simultaneously with production.

As will be apparent to those skilled in the art, many substitutions, alterations and omissions are possible without departing from the spirit or scope of the present invention.

What is claimed is:

l. A method of treating a well having both oil producing and water producing zones to overcome water-coning which comprises, forming a first fracture in the oil producing zone, forming a second fracture in the water/ oil transition zone, cementing said second fracture, forming a third fracture in the water producing zone, dividing the well into an upper portion communicating with said oil zone and a lower portion communicating with said water zone, and injecting a gas under pressure into said lower portion.

2. The method of claim 1 wherein the first fracture, or the third fracture, or both are filled with a propping agent.

3. The method of claim 1 wherein oil recovery from the well is halted before the formation of the fractures and is resumed after injection of the gas.

4. The method of claim 3 wherein gas injection continues after oil production is resumed.

5. The method of claim 3 wherein the injection of gas is halted before oil production is resumed.

6. The method of claim 1 wherein the gas is air.

7. The method of claim 1 wherein the gas is a gaseous mixture of combustion products.

8. The method of claim 1 wherein the gas is natural gas.

References Cited UNITED STATES PATENTS 2,368,424 1/1945 Reistle l66-42 X 2,784,787 3/1957 Matthews et al 166-42 X 2,788,855 4/1957 Peterson l6642 2,832,416 4/1958 Allen l6642 3,032,499 5/1962 Brown l6642 X 3,134,438 5/1964 Huitt et a1 166-42 X 3,228,470 1/1966 Papaila 166-42 X 3,237,690 3/ 1966 Karp et a] 1 66-42 X 3,297,088 1/1967 Huitt et al. 16642 X STEPHEN I NOVOSAD, Primary Examiner. 

